Circuit for starting and operating a gas discharge lamp

ABSTRACT

A circuit is disclosed which is capable of positively shifting a gas discharge lamp from its off-state to its on-state without emitting light flashes and further positively maintains the gas discharge lamp in its on-state when first ignited. The circuit contains an oscillator device which generates and supplies an oscillator signal of a specific oscillator frequency from two output terminals of the oscillator device. It also contains a current limiting device an a parallel-resonance circuit comprising a capacitor and an inductor. The parallel resonance circuit has a frequency of resonance substantially identical to the oscillator frequency. The current limiting device and parallel-resonance circuit are connected in a series configuration across the output terminals of the oscillator device. Further, the gas discharge lamp is connected across or in parallel with the parallel-resonance circuit. The current limiting device preferably constitutes an inductor of a series-resonance circuit, the resonance frequency of which is lower than the oscillator frequency of the oscillator device. The oscillator device is preferably tuned to the frequency of resonance of the parallel-resonance circuit.

The present invention relates to a circuit for starting and operating agas discharge lamp.

A gas discharge lamp is a lamp, which emits light in an electricdischarge in the gas of the gas discharge lamp. In the present context,the term "gas discharge lamp" is a generic term comprising all lampsdifferent from incandescent lamps, such as conventional gas dischargelamps, fluorescent lamps, halide lamps and arc lamps.

Common to all gas discharge lamps is the distinct shift in thecharacteristic of the gas discharge lamp, when the lamp is shifted fromits off-state to its on-state and further the requirement of the gasdischarge lamp of exceeding a threshold of electric energy supply forswitching the gas discharge lamp from its off-state to its on-state. Inits off-state, the gas discharge lamp represents a high electricimpedance, whereas in its on-state the gas discharge lamp represents abasically resistive load or is to be considered equivalent to aresistance of finite value. Since the electric resistance represented bythe gas discharge lamp in its on-state is a decreasing function of theRMS (root mean square) current supplied to the lamp, the lamp has to beconnected with a ballast impedance in series with the lamp itself inorder to limit the current supply to the lamp when the lamp is in itson-state on a constant voltage supply such as a mains supply. From theabove, it is further understood that a starting circuit has to beprovided in order to supply sufficient energy in excess of the abovementioned threshold for shifting the gas discharge lamp form itsoff-state to its on-state.

A plurality of ballast and starter circuit configurations of passive andactive circuit configurations are known in the art. Common to thepassive circuit configurations of the ballast and starter circuits isthe well-known ignition problem resulting in the emission of lightflashes prior to the shift of the gas discharge lamps from theiroff-state to their on-state, as the passive circuit configurations arenot able to positively shift the gas discharge lamps from theiroff-state to their on-state, and the unstable emission of light from thegas discharge lamps often perceived as a constant flickering of thelight emitted. The active circuit configurations of the ballast andstarter circuit known in the art are stated to eliminate the abovestarting and light flickering problems. However, the active circuitconfigurations known hitherto, have gained little commercial success.First this is because highly elaborate circuit configurations areexpensive as compared to more simple passive circuit configurations.Second, it is because stability problems, e.g. when a burnt out gasdischarge lamp is connected to the circuit, may result in excessivecurrent being drawn from the circuit resulting in the destruction of theactive high power components of the circuit.

Therefore, there is a need for a circuit for starting and operating agas discharge lamp in which the circuit on the one hand eliminates theproblems associated with the passive circuit configurations, i.e. whichis capable of positively shifting the gas discharge lamp from itsoff-state to its on-state without emitting light flashes. One is furtherneeded, which, hand, is of a fairly simple configuration as compared tothe active configurations known hitherto. Finally, one is needed whichpositively limits the current or power supplied from the active powersupply components of the circuit when the circuit is connected to a lowimpedance load such as a burnt out gas discharge lamp or a defective gasdischarge lamp. The above object is obtained by a circuit according tothe present invention for starting and operating a gas discharge lamp,comprising:

an oscillator means for generating and supplying an oscillator signal ofa specific oscillator frequency across two output terminals of saidoscillator means,

a current limiting device, and

a parallel-resonance circuit comprising a capacitor and an inductor andhaving a frequency of resonance substantially identical to saidoscillator frequency,

said current limiting device and said parallel-resonance circuit beingconnected in a series configuration across said output terminals, andsaid gas discharge lamp being connected across said parallel-resonancecircuit.

The circuit of the present invention is based on the realization thatthe gas discharge lamp may be started and operated from aparallel-resonance circuit, which is connected in parallel with the gasdischarge lamp, and which is supplied with energy from the oscillatormeans of the circuit through a current limiting device. Consequently,when the gas discharge lamp is in its off-state, and accumulates energy,and when the energy accumulated in the parallel-resonance circuitexceeds the threshold energy for igniting or starting the gas dischargelamp, it supplies a high energy current to the gas discharge lamp as thecurrent limiting device limits the current supplied from theparallel-resonance circuit to the oscillator means and consequentlyprotects the oscillator means from the high energy current.

Apart from fulfilling the above objects of the present invention, thecircuit of the present invention further offers the distinct advantageas compared to commercially available electronic ballast and startercircuits, in that it is capable of positively starting even large orlong fluorescence tubes. This is not possible with known andcommercially available electronic ballast and starter circuits, whichare most often not capable of igniting or starting the fluorescence tubebut only capable of making the tube fluorescent at the ends thereof.

In accordance with the presently preferred embodiment of the circuitaccording to the invention, the current limiting device is constitutedby a further inductor, and the circuit further comprises a furthercapacitor connected in series with said further inductor. Together withthe further inductor, it constitutes a series-resonance circuit. Theseries-resonance circuit has a resonance frequency lower than theoscillator frequency. Since the frequency of resonance of theseries-resonance circuit is lower than the oscillator frequency andconsequently lower than the frequency of resonance of theparallel-resonance circuit, the oscillator signal supplied from theoscillator means is filtered by the series-resonance circuit, therebyattenuating higher order harmonics. Therefore, a basically sinusoidalsignal is supplied to the parallel-resonance circuit and further,provided the gas discharge lamp has been started, supplied to the gasdischarge lamp. This constitutes a basic resistive load, and whichfurther constitutes an aerial, from which the oscillator signal suppliedto the gas discharge lamp is radiated. By filtering the oscillatorsignal and by supplying the sinusoidal signal to the gas discharge lamp,the emission of radio frequency signals, which constitute noise signalsin the radio frequency spectrum, is to a great extent attenuated orsubstantially eliminated. The tuning of the series-resonance circuit toa frequency of resonance lower than the frequency of resonance of theparallel-resonance circuit further provides a varying transformer phasedifference between the series- and parallel-resonance circuits. It alsothe accumulation of energy in the parallel-resonance circuit, when thegas discharge lamp has not yet been started so as to generate a veryhigh starter voltage in the parallel-resonance circuit for starting thegas discharge lamp. Due to the current limiting capability of theinductor of the series-resonance circuit or of the current limitingdevice, the high voltage signal is, as described above, supplied to thegas discharge lamp. This occurs has not yet been started, without anysubstantial energy being re-transferred or re-transmitted to theoscillator means through the series-resonance circuit. The gas dischargelamp is consequently positively started.

It is to be underlined that the voltage generated by theparallel-resonance circuit, when the energy is accumulated in theparallel-resonance circuit, is limited by the Q-factor of theparallel-resonance circuit exclusively. Further, provided the Q-factoris sufficiently high, a starter voltage in excess of the thresholdvoltage required to start the gas discharge lamp may be generated by theparallel-resonance circuit. However, the gas discharge lamp is normallystarted at a voltage far lower than the maximum voltage which may begenerated by the parallel-resonance circuit. This means that thestarting of the gas discharge lamp, and more specifically the startingof gas discharge lamps of different characteristics, viz. of differentstart voltages, is always positively affected by the circuit of thepresent invention.

It has further been realized that the series configuration of theseries-resonance circuit and parallel-resonance circuit, across whichthe gas discharge lamp is connected, provides a substantially constantsupply of energy to the gas discharge lamp independent of theoperational characteristic of the gas discharge lamp, e.g. expressed interms of the voltage of operation of the gas discharge lamp. This may bealtered and, normally will be increased, as the working time oroperational time of the gas discharge lamp increases. The substantiallyconstant supply of energy to the gas discharge lamp, when the gasdischarge lamp is operating, further makes the operation of the gasdischarge lamp independent of the voltage of the oscillator signalgenerated by the oscillator means and further independent of the supplyvoltage supplied to the oscillator means, e.g. from a rectifier means.This will be described below, with the rectifier means further beingconnected to a mains supply.

The circuit of the present invention may, as mentioned above, beemployed for starting and operating any gas discharge lamps, such asfluorescent lamps or tubes, halide lamps, arc lamps, etc. A highlyimportant application of the circuit of the present invention is thestarting and the operation of conventional fluorescence tubes, whichinclude starting electrodes further constituting the terminals of thetubes. In this highly relevant application of the circuit according tothe invention, the series-resonance circuit and the parallel-resonancecircuit may be connected to each other in said series configurationthrough a starting electrode of the gas discharge lamp. By connectingthe resonance circuits to each other through the starting electrode, twoimportant advantages are achieved. First, in the starting phase thecurrent supplied from the series-resonance circuit to theparallel-resonance circuit heats the starting electrode. This promotesthe starting or ignition of the gas discharge lamp. It is, however, tobe underlined that the supply of current to the starting electrode isnot mandatory to the positive starting of the gas discharge lamp bymeans of the circuit of the present invention. Second, the connectionbetween the series-resonance circuit and the parallel-resonance circuitis interrupted when the gas discharge lamp is removed, e.g. for serviceor replacement. When the gas discharge lamp is removed and theconnection between the series-resonance circuit and theparallel-resonance circuit is interrupted, the accumulation of energy inthe parallel-resonance circuit is also interrupted. Thus, when the gasdischarge lamp is removed and the connection between theseries-resonance circuit and the parallel-resonance circuit isinterrupted, the extremely high starting voltage characteristic of theparallel-resonance circuit of the circuit of the present invention isnot generated. This is of the utmost importance from a safety point ofview, as the accumulation of energy in the parallel-resonance circuitmight be of great danger to a person replacing or rearranging the gasdischarge lamp.

In accordance with a further or alternative embodiment of the circuit ofthe present invention, which further reduces the risk of exposing aperson replacing or rearranging the gas discharge lamp to electricshock, the series-resonance circuit and the parallel-resonance circuitare connected to each other in said series configuration through atransformer. A primary winding of the transformer is connected in serieswith the series-resonance circuit across the two output terminals of theoscillator means, and a secondary winding of the transformer isconnected in parallel with the capacitor of the parallel-resonancecircuit so as to constitute the inductor of the parallel-resonancecircuit.

The oscillator means of the circuit according to the invention may beconstituted by, for example, a full-bridge oscillator circuit or,preferably, by a half-bridge oscillator circuit. The output terminals ofthe oscillator means are constituted by a hot terminal and a coldterminal, and the cold terminal further constitutes a ground terminal ofthe entire circuit. The oscillator signal is then supplied from the hotterminal to the series-resonance circuit of the series configuration ofthe series-resonance circuit and the parallel-resonance circuit.

The oscillator means may further be an autonomous operating oscillatormeans, such as a clock controlled oscillator. This supplies theoscillator signal to the series-configuration of the series-resonancecircuit and the parallel-resonance circuit controlled by the clock orcontrolled by any other oscillator controlling means. In this autonomousoscillator means embodiment, the parallel-resonance circuit has,however, to be accurately tuned to the frequency of oscillation, whichis determined internally or externally of the oscillator means. However,the oscillator means is preferably supplied with a feed-back oscillatorsignal for controlling the generation of the oscillator signal. Thefeed-back oscillator signal is generated by the parallel-resonancecircuit to ensure that the oscillator means is tuned to the frequency ofresonance of the parallel-resonance circuit, which makes the tuning ofthe parallel-resonance circuit far less critical and further provides acompensation for temperature variations or temperature drifts, due toe.g. heating or cooling of the capacitor or the inductor of theparallel-resonance circuit.

The feed-back oscillator signal generated in any appropriate manner bythe parallel-resonance circuit may be derived from the current orvoltage oscillating in the parallel-resonance circuit, e.g. from theinductor or from the capacitor or from parts thereof. Further, it maypreferably be generated by a transformer having a primary winding and asecondary winding, the primary winding connecting the capacitor and theinductor of the parallel-resonance circuit, and the secondary windingbeing connected to the oscillator means for supplying the feed-backoscillator signal to the oscillator means.

The half-bridge oscillator preferably constituting the oscillator meansof the circuit according to the invention may be implemented in anyappropriate manner, e.g. comprising valves, coupling transformers, etc.However, the half-bridge oscillator preferably comprises solid stateswitches, such as planar transistors, thyristors, or still morepreferably power MOS-FETs. The half-bridge oscillator comprises at leasttwo solid state switches each having a control terminal, and the abovedescribed transformer generating the feed-back oscillator signal,preferably also comprises two identical secondary windings. The controlterminals of the two solid state switches are connected to a respectivesecondary winding of the transformer for receiving the feed-backoscillator signal so as to control the switches in a push-pulloperation.

The oscillator means, the oscillator frequency of which is preferablytuned to the frequency of resonance of the parallel-resonance circuit,may be controlled into generating and supplying an oscillator signalhaving any appropriate waveform, e.g. a sinusoidal waveform, atriangular waveform or preferably a square-waveform. For controlling theoscillator means into generating the square-wave oscillator signal, thecontrol terminals of the solid state switches may be connected to itsrespective secondary winding of the feed-back oscillator signalgenerating transformer through a peak-limiting circuit so as topeak-limit the feed-back oscillator signal supplied to the controlterminals of the solid state switches. The solid state switches areconsequently operated in an alternating on/off operational moderesulting in the generation of a square-wave oscillator signal. It is,however, to be mentioned that the controlling of the solid stateswitches by means of a single transformer having separate secondarywindings connected to the respective control terminals of the solidstate switches results in a soft shifting of the solid state switches sothat the solid state switches are never turned on at the same time. Thisovershoot or ringing of the oscillator signal waveform, as this mightotherwise result in an excessive current being supplied or drawn fromone or more of the solid state switches. This might further result inthe destruction of one or more solid state switches and in thedestruction of the entire circuit, if not previously eliminated.

The circuit, according to the invention, receives power from a DC powersupply, which may be an internal or an external DC power supply. Inaccordance with the presently preferred embodiment of the circuitaccording to the invention, the oscillator means of the circuitcomprises two input terminals to be connected to a DC power supplyconstituting an external DC power supply for receiving a DC signal fromthe DC power supply. As mentioned above, the circuit according to theinvention may be supplied from a mains supply, and the circuit mayconsequently further comprises or be connected to, the mains supplythrough a rectifier means. This generates the DC power supply signal forthe oscillator means of the circuit.

In a further embodiment of the circuit according to the invention, theDC power supply is constituted by a switch-mode power supply. However,the DC power supply may alternatively be constituted by any appropriateDC power supply means, such as an accumulator means, e.g. a rechargeableaccumulator means including a recharging device or circuit and one ormore rechargeable accumulators, an unstabilized DC power supplyincluding a rectifier and a smoothing capacitor or a stabilized DC powersupply including a rectifier, a smoothing capacitor and a stabilizingcircuit well-known in the art per se. The DC power supply preferablyfurther comprises a filtering means for reducing or eliminating highlyreactive loading of the mains supply in order to reduce the deformationof the sinusoidal wave form of the mains supply voltage due tonon-resistive loading of the mains supply. The filtering means may beconstituted by a conventional mains noise rejection filter.

In order to further reduce the risk of exposing a person replacing orrearranging the gas discharge lamp to even minor electric shocks whichmight confuse the person and in certain replacement or rearrangingsituations be of a great risk to the person, e.g. when the person iscarrying out a rearranging or replacement from a tall ladder, thecircuit preferably further comprises a shut-down circuit connectedacross the gas discharge lamp detecting if the voltage supplied to thegas discharge lamp exceeds a predetermined threshold for a period oftime, exceeding a predetermined period of time. It then disables thecircuit for starting and operating the gas discharge lamp in case thevoltage exceeds the threshold for a period of time exceeding thepredetermined period of time.

A particular feature of the circuit according to the invention is theextremely simple mounting procedure to be carried out when a pluralityof circuits according to the invention are arranged or mounted in alighting fitting or luminaire with a plurality of gas discharge lampsconnected to a respective circuit for starting and operating the gasdischarge lamps.

In the above described presently preferred embodiment of the circuitaccording to the invention, the oscillator means is constituted by ahalf-bridge oscillator having a cold terminal, which constitutes aground terminal of the circuit. The cold terminals or ground terminalsof the individual circuits may consequently be constituted by a commonground terminal from which a single wire connection is to be establishedto one terminal of each of the gas discharge lamps. The gas dischargelamps are further connected to the respective circuits through one ortwo wire connections to a different terminal of a gas discharge lamp inquestion or to the starting electrode of the gas discharge lamp inquestion.

The present invention also relates to a plurality of circuits accordingto the invention, which are further connected to a plurality of gasdischarge lamps in accordance with the above described extremely simplewiring procedure. The plurality of circuits consequently comprises afurther plurality of gas discharge lamps being connected to a respectivecircuit of said plurality of circuits. The ground terminal of each ofthe circuits of the plurality of circuits are constituted by a singleground terminal, and each of the plurality of gas discharge lamps isconnected to the single ground terminal.

The present invention also relates to a balancing transformer forconnecting at least a first and a second gas discharge lamp of a firstand second rating, respectively, in parallel with a common circuit forstarting and operating the gas discharge lamps. The circuit is of arating substantially identical to the sum or ratings of the first. Itfurther contains second gas discharge lamps, a first end of each of thegas discharge lamps being connected to a terminal of said circuit, thebalancing transformer comprising:

a core, and

a first and a second winding,

said first and second windings being arranged on said core, a first endof each of said windings being connected to a common terminal of saidcommon circuit and a second end of each of said windings being connectedto a second end of each of said gas discharge lamps, said windingsfurther being arranged on said core so as to generate a resultingmagnetic field of substantially zero intensity in said core when saidgas discharge lamps are both operating.

The invention will now be further described with reference to thedrawings, in which

FIG. 1 is a schematical view of a presently preferred embodiment of acircuit for starting and operating a gas discharge lamp according to theinvention, connected to a gas discharge lamp constituted by afluorescent tube,

FIG. 2 is a perspective view of a housing containing a circuit boardcomprising the circuit shown in FIG. 1,

FIG. 3 is a schematical view of a plurality of circuits according to theinvention connected to respective gas discharge lamps and to a common DCpower supply illustrating the extremely simple wiring of the circuit andthe gas discharge lamps by employing the circuit according to theinvention,

FIG. 4 is a perspective view of a lightning fitting or luminairecomprising a plurality of circuits and corresponding gas discharge lampsinterconnected in accordance with the wiring shown in FIG. 3,

FIGS. 5a and 5b are schematical views of the wiring of a circuitaccording to the invention to two and four gas discharge lamps,respectively,

FIG. 6 is a perspective view of a lightning fitting or luminaireincluding a circuit according to the invention and two gas dischargelamps interconnected in accordance with the wiring of FIG. 5a.,

FIG. 7 is a schematical view of a slightly modified embodiment of thecircuit for starting and operating the gas discharge lamp shown in FIG.1,

FIG. 8 a schematical view of an alternative part of the circuit shown inFIG. 7 which alternative part includes a transformer,

FIG. 9 a schematical view of a switch-mode DC power supply for thecircuit shown in FIG. 7,

FIG. 10 a schematical view of an alternative DC power supply for thecircuit shown in FIG. 7, and

FIG. 11 a perspective view similar to the perspective view of FIG. 2 ofthe circuit shown in FIG. 7 and the switch-mode DC power supply shown inFIG. 9 arranged on a common printed circuit board to be arranged in acommon housing, not shown in FIG. 11.

In FIG. 1, a presently preferred embodiment of a circuit for startingand operating a gas discharge lamp, such as a flourescence tube, isshown. The circuit is contained within a dotted-line boundary and isdesignated by the reference numeral 10 in its entirety. The gasdischarge lamp is designated the reference numeral 12 and contains twoconventional starting electrodes 14 and 16 arranged at opposite ends ofthe tube. The electronic circuit 10 receives electric power from anexternal DC power supply through power supply rails 18 and 20 andfurther through power supply input terminals 78 and 79, respectively.The electrode 16 of the gas discharge lamp 12 is connected to the inputterminal 79 through a wire 60. The electronic circuit is basically acombination of a half-bridge oscillator and a series connection of aseries-resonance circuit and a parallel-resonance circuit.

The series-resonance circuit is constituted by a capacitor 48 and aninductor 50, and the parallel-resonance circuit is constituted by acapacitor 52 and an inductor 54. As is evident from FIG. 1, theseries-connection between the series-resonance circuit 48, 50 and theparallel-resonance circuit 52, 54 is established through two wires 56and 58 and further through the starting electrode 14 of the gasdischarge lamp or luminescence tube 12. The capacitor 52 and theinductor 54 of the parallel-resonance circuit are further connected toeach other through a primary winding of a feed-back transformer 30,which includes two secondary windings which are connected to arespective part of the oscillator. Centrally, the oscillator comprisestwo power MOS-FET switches 22 and 23, which are connected to therespective feed-back winding of the transformer 30 through resistors 28and 29, respectively. The voltages supplied to the gates of the powerMOS-FET switches 22 and 23 from the feed-back transformer 30 arepeak-limited by peak-limiting devices 24 and 25. These are constitutedby a component known as a "transil" and comprise a series connection oftwo zener diodes, which are connected to each other "back-to-back", i.e.connected to each other through the anodes or, alternatively, thecathodes of the zener diodes. The power MOS-FET switch 22 is furtherconnected to a current limiting circuit constituted by a resistor 44 anda thryristor 26. The oscillator, the oscillation of which is controlledby the feed-back transformer 30 and further tuned to the frequency ofresonance of the parallel-resonance circuit 52, 54 is initially startedby a diac 32, a capacitor 36, which is initially charged and a diode 46.This serves the purpose of blocking the diac after the initial firing ofthe diac and two resistors 40 and 42. The transformer 30 detects anycurrent flowing in the parallel-resonance circuit 52, 54 and shifts thetransistors 22 and 23 from their off-state to their on-state in analternating push-pull mode and further in a mode controlled by thepeak-limiting devices 24 and 25. This is that the oscillating signalsupplied to the series-resonance circuit 48, 50 from the transistors 22and 23 is a square wave oscillator signal. The circuit 10 furtherincludes two de-coupling capacitors 34 and 38.

The circuit 10 operates in the following manner. As mentioned above, theoscillator is initially started by means of the diac 32, the capacitor36, the diode 46 and the resistors 40 and 42 so that the oscillatorstarts transferring electric energy through the series-resonance circuit48, 50 to the parallel-resonance circuit 52, 54. The parallel-resonancecircuit 52, 54 accumulates the energy transferred thereto, consequently,the voltage across the capacitor 52 increases. As mentioned above, thepower MOS-FET switches 22 and 23 are operated so as to generate a squarewave oscillator signal, which results in a maximum power beingtransferred from the power supply rails 18 and 20 to theseries-resonance circuit 48, 50 through the switches 22 and 23. Theseries-resonance circuit 48, 50, the frequency of resonance of which islower than the frequency of resonance of the parallel-resonance circuit52, 54 provides a band-pass filtering of the square wave oscillatorsignal. The signal supplied through the wire 56 is consequently aband-pass filtered signal, i.e. a basically sinusoidal signal, which isof the utmost importance as to limiting of the radiation of radiofrequency noise from the circuit and further from the lamp 12.

The lamp 12 constitutes, in its off-state, an extremely high impedanceand does not, in its off-state provide any loading to theparallel-resonance circuit 52, 54. The signal supplied through the wire56 and further through the starting electrode 14 helps the lamp 12 tostart or initiate as the electrode is heated. However, the main ignitionis affected by the extremely high energy which is accumulated in theparallel-resonance circuit 52, 54, while the lamp 12 is in itsoff-state. When a certain threshold voltage, characteristic of the gasdischarge lamp 12 is increased, the gas discharge lamp is ignited. Asmentioned above, the energy accumulated in the parallel-resonancecircuit 52, 54 results in a generation of an increasing voltage acrossthe capacitor 52. It further results in the voltage across the capacitor52 exceeding the threshold voltage characteristic of the gas dischargelamp 12 after a relatively short period of accumulating energy in theparallel-resonance circuit 52, 54. When the gas discharge lamp startsconducting or ignites, the load of the gas discharge lamp decreases to afairly low resistive impedance of approximately 100 Ω, and the highenergy stored in the parallel-resonance circuit 52, 54 is consequentlydischarged through the gas discharge lamp 12. This ensures that the gasdischarge lamp 12, which has just been started, continues to beconductive and is consequently positively switched from its off-state toits on-state.

After the gas discharge lamp 12 has been started, the oscillation of theoscillator of the circuit 10 is maintained by the parallel-resonancecircuit 52, 54, which controls the generation of the oscillator signalto the gas discharge lamp 12. The parallel-resonance circuit 52, 54further has a stabilizing effect on the gas discharge lamp 12, so thatthe light emitted is perceived as a stable light emission. Furthermore,the series configuration of the series-resonance circuit 48, 50 and theparallel-resonance circuit 52, 54 makes the circuit independent on anyripple on the DC supply, and of any variation of the voltage of the DCsupply. Still further, the voltages across the gas discharge lamp 12 areautomatically stabilized at the operational voltage of the gas dischargelamp since any tendency of the gas discharge lamp 12 to turn off iscounter-acted by the parallel-resonance circuit 52, 54. Thus, in casewhere the gas discharge lamp 12 is about to shift from its on-state toits off-state, which results in a radical increase of the load orimpedance of the gas discharge lamp, the energy transferred from theoscillator through the series-resonance circuit 48, 50 to the parallelconnection of the gas discharge lamp and the parallel-resonance circuit52, 54 is accumulated in the parallel-resonance circuit 52, 54. Thisresults in an increased voltage being applied to the gas discharge lamp12 whereupon the gas discharge lamp 12 shifts back from its off-state toits on-state.

Two additional points are to be emphasized. First, the seriesconfiguration of the series-resonance circuit 48, 50 and theparallel-resonance circuit 52, 54 is established through the startingelectrode 14 of the gas discharge lamp 12. Therefore, in case where thegas discharge lamp 12 is removed from its sockets (not shown in FIG. 1)connected to the wires 56, 58 and 60, the connection between theseries-resonance circuit 48, 50 and the parallel-resonance circuit 52,54 is interrupted. Consequently, the transfer of energy from theoscillator to the parallel-resonance circuit 52, 54 through theseries-resonance circuit 48, 50 is also interrupted, and an extremelyhigh starting voltage accumulated across the capacitor 52 is eliminated.This could otherwise be hazardous to a person replacing the gasdischarge lamp 12 with a new gas discharge lamp or simply remounting thegas discharge lamp after e.g. cleaning. Second, the feed-back of theentire circuit is brought about at the parallel-resonance circuit 52,54. This results in a highly reliable controlling of the oscillatorwithout any risk of overshoot of the oscillator signal supplied from theoscillator and further any risk of rendering the power MOS-FETs 22 and23 conductive at the same time which might else result in excessivecurrent being conducted through the MOS-FETs. The control signal or thefeed-back signal supplied to the oscillator is a true measure of theoscillator signal generated in the high Q parallel-resonance circuit 52,54.

In FIG. 2, a perspective view of a presently preferred integralembodiment of the circuit according to the invention is shown. Thecircuit is housed in a metallic housing designated the reference numeral70 in its entirety. The housing 70 comprises a base housing part 76 anda cover housing part 77. In the base housing part 76, a printed circuitboard 74 is arranged, on which the components of the electronic circuit10 is arranged. Thus, in FIG. 2, the power MOS-FETs 22 and 23, thetransformer 30, the capacitors 36 and 38, the diode 46, the capacitors48 and 52 and the inductors 50 and 54 are shown arranged on the printedcircuit board 74. The terminals 78 and 79, which are accessible from theoutside of the housing 70, are also shown in FIG. 2. The printed circuittracks, not shown in FIG. 2, of the printed circuit board 74, and theelectronic components are insulated in relation to the metallic housingparts 76 and 77 by means of a plastics foil 80. On top of the inductors50 and 54, insulating pads 82 and 81, respectively, are arranged. Fromthe lower side surface of the housing 70, a socket 72 of conventionalconfiguration protrudes. The socket 72 constitutes the connections 56and 58 shown in FIG. 1 and is supported by the circuit board 74 andconnected in electrically conductive connection with circuit tracksthereof.

The integral embodiment shown in FIG. 2 offers a distinct advantage,which will be evident from FIG. 4, viz. that apart from the wireconnections 18 and 20 to the terminals 78 and 79, only a single wireconnection corresponding to the wire 60 shown in FIG. 1 is required forestablishing connection to the circuit and further to the gas dischargelamp connected thereto. In case a plurality of gas discharge lamps and aplurality of circuits are arranged in a lighting fitting or luminaire,only the terminals 78 and 79 of the housing 70 are to be connected inparallel to a common DC power supply, and a single wire 60 is to beconnected from one of the terminals 79 of one of the housings 70 to theindividual electrodes 16 of the gas discharge lamps 12, as is evidentfrom FIG. 3.

In FIG. 3, a diagrammatical view of a circuitry of a lighting fitting orluminaire including a plurality of gas discharge lamps and a pluralityof circuits according to the invention is shown. The individual gasdischarge lamps are connected to the corresponding circuits 10 throughthe wires 56 and 58 and are connected to a terminal corresponding to theterminal 79, shown in FIGS. 1 and 2, or one of the circuits 10 throughthe wire 60. The DC power input terminals 78 and 79 of the circuits 10are connected in parallel to the DC power rails 18 and 20, which arefurther connected to a common DC power supply, which is constituted by abridge rectifier 92, which may be connected to an AC power supply, suchas a 110 V, 220 V or 240 V, 50 Hz or 60 Hz mains supply, throughterminals 90 and 91, a stand-by loading resistor 94, a smoothingcapacitor 96 and a two-way turn-on switch 98, 99. When the switches 98and 99 are open, the capacitor 96 is charged through the resistor 94 toa potential defined by the voltage of the AC power supply signalsupplied to the rectifier 92, as is well known in the art. When theswitches 98 and 99 are activated, the resistor 94 is short-circuited,and the positive DC supply rail 18 is connected through the switch 99 tothe anode of the capacitor 96 and further to the anode of the bridgerectifier 92. The resistor 94, the capacitor 96 and the two-way switch98, 99 serve the purpose of limiting the loading of the bridge-rectifier92 and further of the AC power supply when the entire lighting fittingor luminaire is turned on.

In FIG. 4, a lighting fitting or luminaire designated the refrencenumeral 100 is shown. The lighting fitting or luminaire 100 is alighting fitting of a solarium. The gas discharge lamps 12, which areUV-luminescence tubes, are arranged on the lower side surface of thehousing 100. At the right-hand end of the housing 100, the ends of theindividual UV-luminescence tubes are received in a conventionalluminescence tube socket, to which a single wire 60 is connected inaccordance with the wiring scheme of FIG. 3. In the left-hand end of thehousing 100, the ends of the individual UV-luminescence tubes 12 arereceived in respective sockets 72 of the housings 70 shown in greaterdetail in FIG. 2. The individual housings 70 constituting the abovedescribed integral embodiment of the circuit according to the inventionare connected through their terminals 78 and 79 shown in FIG. 2 to theDC power supply rails 18 and 20 in a parallel configuration. From FIG. 4it is evident that the wiring of the entire assembly of lighting fittingis very simple, well arranged and well planned. This provides a distinctadvantage as compared to the conventional lighting fittings orassemblies for use in solaria. In the conventional embodiment of asolarium, the UV-luminescence tubes are connected to their ballast andstarter circuits through a total of four wires each.

In FIGS. 5a and 5b, a single circuit 10 according to the invention isshown connected to two and four gas discharge lamps, respectively. As isconventional in the art, the circuits for starting and operating the gasdischarge lamp is constructed to a certain power load, e.g. to a 100 Wload. Therefore, a single 100 W circuit according to the invention maystart and operate e.g. two 50 W gas discharge lamps as is shown in FIG.5a or four 25 W gas discharge lamps as shown in FIG. 5b. As is evidentfrom FIG. 5a, the two gas discharge lamps 12 are connected in a seriesconfiguration through the wires 56 and 58 and further a wire 103interconnecting the starter electrodes of the gas discharge lamps 12 towhich starter electrodes the wires 56 and 58 are connected. The starterelectrodes at the opposite ends of the gas discharge lamps 12 areconnected to a bifilarly wound coil 102 through two wires 104 and 105.The bifilarly wound coil 102 serves the purpose of starting andoperating the gas discharge lamps 12 simultaneously. In case the wires104 and 105 were simply connected to the negative power supply rail 20,only one of the gas discharge lamps 12, which are most often notcompletely identical to each other in respect of load characteristics,would presumably be started and therefore operated at an excessive load.However, when one of the gas discharge lamps 12 is ignited or started,the bifilarly wound coil 102 increase the voltage across the other gasdischarge lamp which is consequently also started. Furthermore, the coil102 stabilizes the operation of the two gas discharge lamps 12 in thatany drift of one of the two tubes or lamps, which could cause the otherlamp or tube to be turned off, is compensated for by the bifilarly woundcoil. This increases the voltage across the lamp or tube, which is aboutto be turned off, and consequently forces the lamp or tube back intooperation or steadily maintains the lamps or tubes in their on-state.

In FIG. 5b the gas discharge lamps or tubes 12 are also connected in aseries configuration through the wires 56 and 58 and further throughwires 113, 114 and 115. Apart from the bifilarly wound coil 102 and thewires 104 and 105, which serve the purpose of splitting the four lampsor tubes into two sets of each two lamps or tubes, the assembly includestwo additional bifilarly wound coils 106 and 108 corresponding to thecoil 102 and wires 109, 110, 111 and 112. These are for establishingconnection between the coils 106 and 108 and the individual lamps ortubes 12. Basically, the four lamp embodiment shown in FIG. 5b functionsin the same manner as the embodiment shown in FIG. 5a.

In FIG. 6, a perspective and exploded view of a lighting fitting orluminaire of the wiring scheme configuration of FIG. 5a is shown. InFIG. 6, the gas discharge lamps or tubes 12 are received in separatesockets 121, which are mounted in a lighting fitting or luminairehousing 120. In the housing 120, the electronic circuit 10 according tothe invention, the DC power supply capacitor 96 and the bifilarly woundcoil 102 are also contained. In an alternative embodiment, the DC powersupply capacitor 96 and the bridge rectifier, not shown in FIG. 6, arealso housed in the housing containing the circuit 10.

In FIG. 7, a slightly modified embodiment relative to the embodiment ofthe circuit 10 shown in FIG. 1 is shown designated the reference numeral10' in its entirety. The circuit 10' basically includes the same circuitconfiguration and the same components as shown in FIG. 1 and describedabove. The circuit 10' shown in FIG. 7, however, differs from thecircuit 10 shown in FIG. 1 in the following aspects: Firstly, thesmoothing input capacitor 34, the decoupling capacitor 38 and theresistor 42 are omitted. Secondly, the power MOS-FET switch 23 isprovided with a current limiting circuit constituted by a thyristor 126and a resistor 144 corresponding to the thyristor 26 and the resistor44, respectively, connected to the power MOS-FET switch 22. Thirdly, theorder of the capacitor 48 and the inductor 50 of the series-resonancecircuit is changed. Fourthly, the circuit 10' shown in FIG. 7 isprovided with a resistor 132 connected in series with the diode 46, thenode of the cathode of the diode 46 and one of the terminals of theresistor 132 being connected to a terminal 141, the importance of whichwill be described below. A resistor 134 is further providedinterconnecting a further terminal 142 also to be described in detailbelow and the node of the diac 32 and the gate of the power MOS-FETswitch 23. In FIG. 7, the wires 56, 58 and 60 are further connected toterminals 138, 139 and 140, respectively, of a multi-pole terminal blockor socket 136.

Fifthly, in the lower part of FIG. 7, a shut-down circuit is providedwhich shut-down circuit is included in a dotted line boundary block andserves the purpose of determining if the voltage generated by theparallel resonance-circuits 52, 54 and supplied to the terminal 139through the wire 58 exceeds a predetermined threshold for a period oftime which exceeds a predetermined period of time. This corresponds tothe situation in which the circuit 10' for starting and operating thegas discharge lamp connected to the circuit 10' through the terminals138, 139 and 140 does not ignite or is not able to be shifted from itsoff-state to its on-state, e.g. because of the fact that the gasdischarge lamp has been burned out or that wires have been broken ordisconnected. The shut-down circuit serves two purposes: Firstly, thepurpose of protecting a person replacing the gas discharge lamp whichdoes not ignite from exposure to electric shock, and secondly, thepurpose of protecting the entire circuit 10' for starting and operatingthe gas discharge lamp from excessive currents and voltages.

The shut-down circuit comprises the following components: a resistor146, a diode 147, a diode 148, a resistor 149, a capacitor 150, aresistor 151, a capacitor 152, a resistor 153, a diac 154, a resistor155, a capacitor 156, a capacitor 157, a thyristor 158, and a thyristor128. Basically, the diodes 147 and 148 serve the purpose of rectifyingthe high frequency altering voltage supplied to the gas discharge tubefrom the parallel-resonance circuits 52, 54, which voltage is generatedacross the terminals 139 and 140. The rectified voltage is charged onthe capacitor 150, the charging time constant being determined by theresistor 146 and the capacitor 150. The resistor 151 and the capacitor152 constitute a low-pass filter for filtering out any excessive highvoltage spikes.

Provided the voltage across the terminals 138 and 140 has exceeded apredetermined threshold determined by the diac for a period of timeexceeding the time required for charging the capacitor 152 to saidthreshold, the diac 154 fires and consequently turns on the thyristor158 which draws current from the terminal 78 through the resistor 153and turns on the thyristor 128 which is connected in parallel with thethyristor 126 and is maintained in a conducting state until the entirecircuit has been shut off, due to the current supplied to the thyristorthrough the resistor 163, so that the power MOS-FET 23 has its gateshort-circuited to the terminal 79 through the thyristor 128.

In FIG. 8, a slightly modified configuration of the the seriesconfiguration of the series-resonance circuits 48, 50 and theparallel-resonance circuit characteristic of the present invention isshown. In FIG. 8, the parallel-resonance circuit is constituted by asecondary winding of a transformer 160 and two capacitors 161 and 162which are connected between the terminals 138 and 139 and between theterminals 139 and 140, respectively. The primary winding of thetransformer 160 is connected in series with the series-resonance circuit48, 50 across the output terminals of the half-bridge oscillator. By theprovision of the transformer 160, the gas discharge lamp connected tothe circuit through the terminals 138, 139 and 140 is galvanicallyseparated from the circuit for starting and operating the gas dischargelamp and further from the DC power supply which is still furtherconnected to the mains supply, as will be described below, which DCpower supply supplies DC power to the circuit for starting and operatingthe gas discharge lamp. Consequently, the transformer 160 galvanicallyseparates the terminals 138, 139 and 140 and, consequently, the gasdischarge lamp from the mains supply. The capacitors 161 and 162 providea voltage division of the voltage generated across the terminals 138 an140. Consequently, a voltage is generated across the gas discharge lampconnected thereto so as to generate a small voltage across the capacitorand consequently the starting electrode of the gas discharge lampconnected to the terminals 138 and 139 from the high ignition voltagegenerated across the terminals 138 and 140. Furthermore, the transformercoupling shown in FIG. 8 renders it possible to connect a number of gasdischarge lamps to a single circuit for starting and operating the gasdischarge lamps by means of individual transformers or separatesecondary windings of the transformer 160.

As indicated above, the above described circuits 10 and 10' shown inFIGS. 1 and 7, respectively, may be supplied from any appropriate DCpower supply, e.g. the DC power supply shown in the left hand side ofFIG. 3 which may constitute a DC power supply common to a plurality ofcircuits for starting and operating individual gas discharge lamps ormay constitute a DC power supply for a single circuit for starting andoperating a gas discharge lamp. With reference to FIGS. 9 and 10 astabilized, switch-mode DC power supply and an unstabilized DC powersupply, respectively, for the above described circuit 10' shown in FIG.7 is to be described.

The switch-mode DC power supply shown in FIG. 9 is designated thereference numeral 180 in its entirety. For providing electricalconnection to the mains supply, the switch-mode power supply circuit 180is provided with an AC mains supply plug or terminal block 163comprising a live terminal 164 and a neutral terminal 165. The liveterminal 164 is connected to a fuse 166 and further through athermostatically controlled switch 167 to a capacitor 168 which is alsoconnected to the neutral terminal 165. The capacitor 168 is consequentlyconnected across the terminals 164 and 165 and further across a radiofrequency interference filter 169 comprising two windings on a commoncore. Across the radio frequency interference filter 169, a voltagedependent resistor 170 and a full-wave bridge rectifier 171 areconnected. Across the positive and negative terminals of the full-wavebridge rectifier 171, which serves the purpose of rectifying the mainsvoltage supplied to the full-wave bridge rectifier 171 from theterminals 164 and 165, a smoothing and radio frequency interferencesuppression capacitor 172 is connected.

The negative terminal of the full-wave bridge rectifier 171 is connectedto the above-mentioned terminal 79, and the positive terminal of thefull-wave bridge rectifier 171 is connected to the above describedterminal 78 through an inductor 173 and a diode 174. The switch-mode DCpower supply circuit 180 centrally comprises an integrated circuit 175of the type TDA 4814A manufactured by the company Siemens AG. As far asthe integrated electronic circuit 175 of the type TDA 4814A isconcerned, reference is made to the descriptions and application notesfrom Siemens AG, referring to the integrated circuit of the type TDA4814A.

From the positive terminal of the full-wave bridge rectifier 171 areference voltage is derived by means of a resistive divider networkcomprising three resistors 176, 177 and 178 and further a smoothingcapacitor 179, which reference voltage is supplied to the multiplierreference input terminal 11 of the integrated circuit 175. Theintegrated circuit 175 has its terminal 1 connected to the negativeterminal or ground terminal 79. The series-resonance circuit comprisinga resistor 181 and a capacitor 182 is connected between the terminals 12and 13 of the integrated circuit 175, which terminal 12 of theintegrated circuit 175 is further connected to the terminal 78 of the DCswitch-mode power supply circuit 180 through two resistors 183 and 184.Across the terminals 78 and 79, a capacitor 185 is arranged whichcapacitor basically corresponds to the capacitor 34 shown in FIG. 1.

The node of the resistors 183 and 184 is further connected to theterminal 79 through a resistor 186. The switch-mode DC power supplycircuit 180 further includes a power MOS-FET switch 187, the gate ofwhich is connected to the terminal 2 of the integrated electroniccircuit 175, the drain of which is connected to the node of the inductor173 and the anode of the diode 174, and the source of which is furtherconnected to the terminal 4 of the integrated electronic circuit 175.The terminal 4 is further connected to the ground terminal 79 through aresistor 188. The switch-mode DC power supply circuit 180 furthercomprises a smoothing capacitor 189, two diodes 190, 191, whichconstitute a switch-mode circuit configuration, and a capacitor 192which is connected to the terminal 141. The terminal 142 is connected tothe terminal 14 of the integrated electronic circuit 175. As is evidentfrom FIG. 9, the cathode of the diode 191 is connected to the terminal 3of the integrated electronic circuit 175.

It is to be realized that the integrated electronic circuit 175 is notturned on until the circuit 10' shown in FIG. 7 connected to theswitch-mode DC power supply circuit 180 through the terminals 78, 79,141 and 142 has started its oscillation. As is evident from FIG. 9, theinternal DC input terminal 3 of the integrated electronic circuit 75 isconnected to the capacitor 189. The capacitor 189 is loaded through thediodes 190 and 191 and further through the capacitor 192 from theterminal 141 connected to the circuit 10' for starting and operating thegas discharge lamp. The voltage supplied from the circuit 10' to theterminal 141 is the oscillator signal generated by the power MOS-FETswitches 22 and 23 which oscillator signal is transferred through thecurrent limiting device or inductor 50 to the parallel-resonancecircuits 52, 54 in accordance with the teaching of the presentinvention.

As is evident from FIGS. 7 and 9, the terminal 14 of the integratedelectronic circuit 175 is connected to the gate of the power MOS-FETswitch 23 and, consequently, constitutes a feed back loop from theoscillator of the circuit 10' to the detector input terminal 14 of theintegrated electronic circuit 175. On the basis of the comparison of thevoltage present on the terminal 11 of the integrated electronic circuit175 which voltage respresents the mains supply voltage, and the voltagepresent of the terminal 12 of the integrated electronic circuit 175which voltage represents the voltage across the capacitor 185, theflip-flop of the integrated electronic circuit 175 switches the powerMOS-FET switch 187 on and off in order to draw current from the positiveterminal of the full-wave bridge rectifier 171 so as to draw currentthrough the inductor 173. This occurs when the power MOS-FET switch 187is turned on which current results in the accumulation of energy in theinductor. When the power MOS-FET switch 187 is turned off, the energystored in the inductor is transferred to the capacitor 185 through thediode 174. By this operation the voltage across the capacitor may beincreased above the voltage across the capacitor 172. This operation isalso known as "booster" operation. The circuit 180 shown in FIG. 9provides a very low reactive loading of the mains supply and further ahigh power factor in that the current drawn from the mains supply is inphase with the mains supply voltage.

In FIG. 10, an alternative DC power supply circuit designated thereference numeral 180' is shown. The DC power supply circuit 180' shownin FIG. 10 is basically an unstabilized DC power supply circuit. Thisdiffers from the above described stabilized or switch-mode power supplycircuit 180 shown in FIG. 9 in that the components 172-178 and thecomponents 181-192 are omitted, and further in that a further capacitor198 and a further radio frequency interference filter 199 areinterconnected between the radio frequency interference filter 169 andthe voltage dependent resistor 170 in order to further suppress noise onthe mains supply generated by the circuit 180' and further the circuit10' shown in FIG. 7. The circuit 180' shown in FIG. 10 further comprisesa resistor 193 which is connected between the positive terminal of thefull-wave bridge rectifier 171 and the terminal 78 constituting aresistive load to the full-wave bridge rectifier during the starting ofthe circuit 10', a triac 194, which has it gate terminal connectedthrough a resistor 195 to the terminal 141 and which is consequentlyturned on like the above described integerated electronic circuit 175after the circuite 10' has started its oscillating operation by whichturn-on of the triac 194 the load resistor 193 is short-circuited.Across the terminals 78 and 79 two smoothing capacitors 196 and 197 areconnected. It is to be realized that the resistor 193, the capacitors196 and 197 and the triac 194 basically serve the same purpose as theresistor 94, the capacitor 96 and the switches 98, 99 of the powersupply circuit shown in FIG. 3.

In FIG. 11, a perspective view of an implementation of the electroniccircuits 10' and 180 shown in FIG. 7 and in FIG. 9, respectively, isshown. In FIG. 11 the components: 48, 50, 52, 54, 23, 35, 126, 202, 185,175, 173, 172, 170, 189, 168, 167, 166 and 163 are shown arranged on aprinted circuit board 200. In the embodiment shown in FIG. 11 theprinted circuit board 200 is constituted by a single-sided printedcircuit board of a conventional structure. As is evident from FIG. 11,all the components of the circuits 10' and 180, shown in FIG. 7 and inFIG. 9, respectively, are mounted on the printed circuit board 200.Thus, the assembly constituted by the printed circuit board 200 and thecomponents arranged thereon are adapted to be arranged in a housingwhich may be constituted by an aluminum housing or preferably a housingof an insulating material such as a housing cast from a strong plasticsmaterial such as the material LEXAN, from which housing the multipoleterminals 136 and 163 protrude for providing access, and in whichhousing the above-mentioned assembly is secured and maintained inposition by a moulding compound filling the entire space of the housing.The moulding compound is preferably a heat conducting compound as iswell-known in the art for thermally stabilizing the entire circuitry andfurther for conducting heat to the outer side surfaces of the housing.The outer side surfaces of the housing may further be provided with heatradiating fins or ribs for increasing the surface area of the housing.As is evident from FIG. 11, the power MOS-FETs 22, 23 and 187 aremounted on heat sinks 201, 202 and 203, respectively.

EXAMPLE 1

An 100 W implementation of the circuit shown in FIG. 1 was constructedfrom the following components:

The capacitor 34 was constituted by a 2.2 μF/400 V capacitor,

the resistor 40 was a 1 MΩ resistor,

the resistor 42 was a 330 kΩ resistor,

the capacitor 38 was a 1 nF capacitor,

the capacitor 36 was a 100 nF capacitor,

the diode 40 was a diode of the type 1N4847,

the diac 32 was a diac of the type 1N5758,

the power MOS-FETs 22 and 23 were power MOS-FETs BUZ 76,

the peak-limiting devices 24, 25 were transils of the type BZW12B,

the resistor 44 was a 0.25 Ω resistor,

the thyristor 26 was 2N 5061 thyristor,

the resistors 28 and 29 were 100 Ω resistors,

the capacitor 48 of the series-resonance circuit was a 100 nF/1200 Vcapacitor,

the inductor 50 of the series-resonance circuit was a 600 μH inductorconstitued by 60.5 windings of wire on a ferrite coil core,

the capacitor 52 of the parallel-resonance circuit was a 47 nF/1200 Vcapacitor,

the inductor 54 of the parallel-resonance circuit was a 270 μH inductorconstituted by 43.5 windings of wire on a ferrite coil core, and

the transformer 30 was wound on a ferrite ring comprising a singleprimary winding and two secondary windings including 20 windings each.

EXAMPLE 2

220 V/50 Hz, 100 W and a 240 V/50 Hz, 100 W implementations of acombination of the circuits shown in FIGS. 7 and 10 were constructedfrom the following components:

The fuse 166 was a 3 A fuse,

the thermostatically controlled switch 167 was a 85° C., 5% temperatureprotector,

the terminal block 163 was a 2-pole terminal block, min 10 A,

the terminal block 136 was a 3-pole terminal block, min. 10 A,

the capacitors 168 and 198 were 100 nF, min 250 VAC capacitors,

the radio frequency interference filters 169 and 199 were RFI-filters,min. 1 A,

the voltage dependent resistor 170 was a VDR, 250 V,

the full-wave bridge rectifier 171 was a 1 A, min. 600 V (220 V/50 Hz)or 700 V (240 V/50 Hz) rectifier,

the resistor 193 was a 100 Ω, Wire Wound, 4 W resistor,

the resistor 195 was a 10 Ω, 1 W, 5% resistor connected in series with a1 nF, 400 V capacitor,

the capacitors 196 and 197 were 47 μF, 350 V electrolytic capacitors,min 105° C.,

the triac 194 was a 400 V, min. 10 A triac,

the resistors 146 and 149 were 1 MΩ, metal film, 0.5 W, 1% resistors,

the resistor 132 was a short-circuit connection,

the resistor 134 was omitted,

the resistor 153 was a 33 kΩ, min. 2.5 W, 5% resistor,

the resistor 155 was a 10 kΩ, metal film, min. 0.5 W, 1% resistor,

the capacitor 152 was a 220 nF, 63 V capacitor,

the resistors 40 and 151 were 5.6 MΩ metal film, min. 0.5 W, 1%resistors,

the capacitors 36, 150, 156 and 157 were 100 nF 163 V capacitors,

the diodes 46, 147 and 148 were diodes of the type 1N4847,

the diacs 32 and 154 were 32 V, 10% diacs,

the power MOS-FETs 22 and 23 were 400 V power MOS-FETs, min. 3 A, max.1.5 Ω,

the peak-limiting devices 24, 25 were 15 V transils,

the resistors 44 and 144 were 0.18 Ω resistors, metal film, min. 0.5 W,1%,

the thyristors 26, 120, 126 and 158 were min. 400 V, lh<3 mA, 630<Vt<680mV thyristors,

the resistors 28 and 29 were 100 Ω metal film, min. 0.5 W, 1% resistors,

the capacitor 48 of the series-resonance circuit was a 100 nF, min. 400V polyester, 10% capacitor,

the inductor 50 of the series-resonance circuit was a 600 μH inductor,min. 2 A, Q>200,

the capacitor 52 of the parallel-resonance circuit was a 47 nF, min. 100V polyester, 5% capacitor,

the inductor 54 of the parallel-resonance circuit was a 270 μH inductor,min. 4 A, Q>200,

the transformer 30 was wound on a ferrite ring comprising a singleprimary winding and two secondary windings including 20 windings each.

EXAMPLE 3

120 V/60 Hz, 33 W, 120 V/60 Hz, 100 W and 220 V/50 Hz, 100 Wimplementaions of combinations of the circuits shown in FIGS. 7 and 9(for 120 V/60 Hz, 33 W modified in accordance with FIG. 8) wereconstructed from the following components:

The terminal block 136 was a 3-pole terminal block, min. 10 A,

the terminal block 163 was a 2-pole terminal block, min. 10 A,

the fuse 166 was a 3 A fuse,

the thermostatically controlled switch 167 was a 85° C., 5% temperatureprotector,

the resistors 40 and 151 were 5.6 MΩ resistors,

the capacitors 36, 150, 156, 157 and 179 were 100 nF capacitors, min 25V,

the diodes 46, 147 and 148, 190 and 191 were diodes of the type 1N4847,

the diacs 32 and 154 were 32 V, 10% diacs,

the power MOS-FETs 22, 23 and 187 were 400 V power MOS-FETs, min. 3 A,max. 1.5 Ω(for 220 V/50 Hz,

the power MOS-FET 187 was a 500 V power MOS-FET, min. 2 A, max. 1.5 Ω),

the peak-limiting devices 24, 25 were 15 V transils,

the resistors 44 and 144 were 0.18 Ω resistors,

the thyristors 26, 126, 128 and 158 were min. 400 V, lh<3 mA, 630mm<Vt<680 mV thyristors,

the resistors 28 and 29 were 100 Ω resistors,

the capacitor 168 was a 100 nF, min. 250 VAC capacitor,

the radio frequency interference filter 169 was a RFI-filter, min. 1 A(120 V, 60 Hz, 100 W), or min. 0.5 A (120 V, 60 Hz, 33 W and 220 V, 50Hz, 100 W),

the voltage dependent resistor 170 was a VDR, 250 V,

the full-wave bridge rectifier 171 was a 1 A, min. 600 V (120 V, 60 Hz)or 700 V (220 V, 50 Hz) rectifier,

the capacitor 172 was a 2.2 μF, 400 V polyesther capacitor,

the inductor 173 was a 1 mH, min. 2 A inductor (120 V/60 Hz), or a 2 mH,min. 1 A inductor (220 V/50 Hz),

the diode 174 was a fast, min. 1 A, min. 400 V, max. 50 nS diode,

the integrated electronic circuit 175 was a TDA 4814A (Siemens AG),

the resistor 153 was a 33 kΩ, metal film, min. 2.5 W, 5% resistor,

the resistors 132 and 177 were 10 Ω resistors,

the resistor 134 was a 100 kΩ resistor,

the resistors 146 and 149 were 1 MΩ resistors,

the resistors 155 and 178 were 10 kΩ resistors,

the capacitors 152, 179 and 182 were 220 nF, min. 63 V (100 W) or min.25 V (33 W) capacitors,

the resistors 181, 183 and 186 were 2 kΩ resistors,

the resistor 184 was a 301 kΩ resistor (for 120 V/60 Hz, 53 W and 100 W)or a 330 kΩresistor (for 220 V/50 Hz, 100 W),

the capacitor 185 was a 47 μF, 350 V, electrolytic capacitor, min. 105°C.,

the resistor 188 was a 22 Ω resistor (for 120 V/60 Hz, 33 W and 100 W)or a 56 Ω resistor (for 220 V/50 Hz, 100 W),

the capacitor 189 was a 100 μF, 16 V, electrolytic capacitor, min. 105°C.,

the capacitor 192 was a 1 nF, 400 V capacitor,

the capacitor 48 of the series-resonance circuit was a 100 nF, min. 250V (33 W) or min. 400 V (100 W) capacitor,

the inductor 50 of the series-resonance circuit was a 600 μH inductor,min. 2 A, Q>200 (100 W) or a 900 μH, min. 1 A, Q>200 (33 W),

the capacitor 52 or the capacitor 102 of the 120 V/60 Hz, 33 Wimplementation of the parallel-resonance circuit was a 47 nF, min. 1000V, 5% polyester capacitor,

the capacitor 161 of the 120 V/60 Hz, 33 W implementation was a 680 nF,min. 25 V capacitor,

the inductor 54 of the parallel-resonance circuit was a 270 μH inductor,min. 4 A, Q>200 (100 W) or a 500 μH, min 1 A, Q>200 (33 W), and

the transformer 30 was wound on a ferrite ring comprising a singleprimary winding and two secondary windings including 20 windings each.

In the above examples 1, 2 and 3, the resistors were min. 0.5 W, 1%metal film resistors if not otherwise specified.

The circuit of the above examples had the following characteristics. Thefrequency resonance of the parallel-resonance circuit 52, 54 was 40-45kHz, the frequency of resonance of the series-resonance circuit 48, 50was 20-25 kHz. The ignition voltage generated by the parallel-resonancecircuit 52, 54 was approximately 2 kV. The operational voltage generatedby the circuit and supplied to the gas discharge lamp was approx.100-125 V dependent on the age of the gas discharge lamp, howeverindependent of the DC supply voltage varying between 270 V and 310 V.The oscillator frequency was basically determined by the frequency ofresonance of the parallel-resonance circuit 52, 54, and the frequency ofresonance and further the oscillator frequency was basically constantduring start, operation and throughout the operational time.

Apart from the above described advantages as to the positive starting ofthe luminescence tube connected to the circuit, the avoided lightflickering, the low radio frequency emission, the well planned and wellarranged wire connection, the embodiment of the above example hasfurther disclosed the following advantages. The power requirements ofthe lighting fitting is 25-30% lower than the power requirements of aconventinal lighting fitting including a passive ballast and startercircuit and the life-time of the gas discharge lamp or the luminescencetube powered by the circuit according to the invention seems to beincreased at least by a factor of 1.5-2. These advantages are believedto have their origin in the high frequency operation of the gasdischarge lamp and the fact that the gas discharge lamp, which ispowered by the circuit according to the invention, is supplied with aconstant power signal due to the series configuration of theseries-resonance circuit and the parallel-resonance circuit, acrosswhich the gas discharge lamp or luminescence tube is connected.

Although the invention has been described with reference to a specificembodiment, it is obvious to the skilled art worker that numerousmodifications may easily be deduced from the teachings of the presentinvention. Thus, the oscillator of the circuit of the present inventionmay be modified into a full-bridge oscillator by connecting the starterelectrode 16 shown in FIG. 1 to a circuit similar to the circuit 10shown in FIG. 1. Such modifications are to be considered covered by thescope of the appending claims. Furthermore, although the invention hasbeen described with reference to a particular application of the circuitof the present invention, viz. in connection with luminescence tubes, itis, however, believed that the circuit of the present invention may alsobe adapted to start and operate arc lamps and halide lamps andconsequently any discharge lamp of the above described generic type,which are distinguishable from incandescent lamps.

I claim:
 1. A circuit for starting and operating a gas discharge lamp,comprising:a series-resonance circuit comprising a first capacitator anda first inductor; a parallel-resonance circuit, comprising a secondcapacitor and a second inductor, said series-resonance circuit having aresonance frequency lower than that of said parallel-resonance circuit;and oscillator means, connected to said series-resonance circuit, forgenerating and supplying an oscillator signal of a specific oscillatorfrequency, substantially identical to said resonance frequency of saidparallel-resonance circuit, to said gas discharge lamp through saidseries-resonance circuit, said series-resonance circuit and saidparallel-resonance circuit being connected in a series configuration. 2.A circuit as claimed in claim 1, wherein said series-resonance circuitband-pass filters said oscillator signal supplied by said oscillatormeans.
 3. A circuit, as claimed in claims 1 or 2 wherein saidseries-resonance circuit and said parallel-resonance circuit areconnected to each other in said series configuration through a startingelectrode of said gas discharge lamp.
 4. A circuit, as claimed in claim1, wherein said oscillator means is supplied with a feed-back oscillatorsignal for controlling the generation of said oscillator signal, saidfeed-back oscillator signal being generated by said parallel-resonancecircuit.
 5. A circuit, as claimed in claim 1, wherein said oscillatormeans has two input terminals for connection to a DC power supply forreceiving a DC power supply signal and two output terminals forgenerating and supplying said oscillator signal.
 6. A circuit, asclaimed in claim 5, further comprising said DC power supply and arectifier means for connection to a mains supply.
 7. A circuit, asclaimed in claim 6, wherein said DC power supply is constituted by aswitch-mode power supply.
 8. A circuit, as claimed in claim 1, furthercomprising a shut-down circuit connected in parallel with said gasdischarge lamp for detecting whether the voltage supplied to said gasdischarge lamp exceeds a predetermined threshold for a period of timeexceeding a predetermined period of time and for disabling said circuitfor starting and operating said gas discharge lamp in case said voltageexceeds said threshold for a period of time exceeding said predeterminedperiod of time.
 9. A circuit, as claimed in claim 1, wherein saidoscillator means is supplied with a feed-back oscillator signal forcontrolling the generation of said oscillator signal, said feed-backoscillator signal being generated by said parallel-resonance circuit andsaid oscillator means generates and supplies a square wave oscillatorsignal.
 10. A circuit as claimed in claim 9, wherein saidseries-resonance circuit and parallel-resonance circuit are connected toeach other in said series configuration across output terminals of theoscillator means.
 11. A circuit for starting and operating a gasdischarge lamp, comprising:a series-resonance circuit comprising a firstcapacitor and a first inductor; a second capacitor; oscillator meansconnected to said series-resonance circuit, including a transformerhaving a primary winding and a secondary winding, said primary windingof said transformer being connected in a series configuration with saidseries-resonance circuit, and said secondary winding of said transformerbeing connected in parallel with said second capacitor constituting aparallel-resonance circuit having a frequency of resonance lower thanthat of said series-resonance circuit, said oscillator means generatingand supplying an oscillator signal, of a frequency substantiallyidentical to said resonance frequency of said parallel-resonancecircuit, to said gas discharge lamp.
 12. A circuit, as claimed in claim11, wherein said series-resonance circuit band pass filters saidoscillator signal supplied by said oscillator means.
 13. A circuit forstarting and operating a gas discharge lamp, comprising:series-resonancecircuit comprising a first capacitor and a first inductor;parallel-resonance circuit comprising a second capacitor and a secondinductor resonance circuit, said series-resonance circuit having afrequency of resonance lower than that of said parallel-resonancecircuit; oscillator means, connected to said series resonance circuit,constituted by a half-bridge oscillator circuit, for generating andsupplying an oscillator signal of a specific oscillator frequency,substantially identical to said resonance frequency of saidparallel-resonance circuit, across a hot terminal and a cold terminalconstituting a ground terminal of said circuit, to said gas dischargelamp through said series-resonance circuit; said series-resonancecircuit and said parallel-resonance circuit being connected in a seriesconfiguration across said hot and cold terminals.
 14. A circuit, asclaimed in claim 13, wherein said oscillator means constituted by ahalf-bridge oscillator circuit generates and supplies a square waveoscillator signal.
 15. A circuit, as claimed in claim 13, wherein saidseries-resonance circuit and said parallel-resonance circuit beingconnected to each other in said series configuration through a startingelectrode of said gas discharge lamp.
 16. A circuit, as claimed in claim13, wherein said oscillator means is supplied with a feed-backoscillator signal for controlling the generation of said oscillatorsignal, said feed-back oscillator signal being generated by saidparallel-resonance circuit.
 17. A circuit, as claimed in claim 16,wherein said series-resonance circuit and said parallel-resonancecircuit are connected to each other in said series configuration througha starting electrode of said gas discharge lamp.
 18. A circuit, asclaimed in claims 2 or 16, wherein said oscillator means is constitutedby a half-bridge oscillator circuit and generates and supplies a squarewave oscillator signal.
 19. A circuit, as claimed in claim 18, whereinsaid series resonance circuit and said parallel-resonance circuit areconnected to each other in said series configuration through a startingelectrode of said gas discharge lamp.
 20. A circuit, as claimed in claim18, wherein said feed-back oscillator signal is generated by atransformer comprising a primary winding and a secondary winding, saidprimary winding interconnecting said capacitor and said inductor of saidparallel-resonance circuit, and said secondary winding being connectedto said oscillator means for supplying said feed-back oscillator signalto said oscillator means.
 21. A circuit, as claimed in claim 20, whereinsaid half-bridge oscillator comprises at least two solid state switcheseach having a control terminal, said transformer comprises two identicalsecondary windings, and said control terminals are connected to arespective secondary winding of said transformer for receiving arespective feed-back oscillator signal for controlling said switches ina push-pull operation.
 22. A circuit, as claimed in claim 21, wherein apeak-limiting circuit is interconnected between each of said controlsignals and its respective secondary winding for peak-limiting saidfeed-back oscillator signal supplied to each of said control terminalsfor controlling said oscillator means to generate a square waveoscillator signal.